Due to the great leap forward in semiconductor IC technology, cellular phones, electronic information terminals, laptop computers, and other portable small-sized and lightweight electronic information equipment have been developed. Every 18 months, the assembly density of the microprocessor doubles. Based on this rule known as Moore's law, the number of transistors assembled in each semiconductor chip is on the rise each year. On the other hand, the package size of the conventional semiconductor devices, such as QFP (Quad Flat Package) and SOJ (Small Out-line J-leaded Package) is larger than semiconductor chips that are several millimeters to just over tens of millimeters in size. This hampers a further increase in the density of the electrode parts and further miniaturization of the electrode information equipment.
CSP (Chip Size Package) is a type of package with an increased density so that the size of the IC package is identical or slightly larger than that of the chip. At present, various. types of CSP semiconductor devices have been proposed. However, there is a problem with the mass production of CSP, that is, its manufacturing cost is higher than that of QFP and other conventional packages. The boosting in the cost of the package is mainly due to the complicated structure and increased number of manufacturing steps.
As a form of the CSP type of semiconductor device, a semiconductor chip is carried on an insulating substrate, with the principal surface of the semiconductor chip facing upward, then wire bonding is performed to connect the conductor leads on the substrate and the electrode pads of the chip. In this case, because the electrode pads, conductor leads, and conductor wires connecting them cannot be exposed to air, it is necessary to completely cover them with a resin. However, sealing with a resin leads to an increase in the thickness of the package, and the heat releasing property of the semiconductor chip deteriorates. In addition, the aforementioned structure has been used in practice on memory IC and other so-called center-bond-type semiconductor chips having a column of electrode pads at the center of the chip's principal surface.
On the other hand, there is the so-called flip chip assembly type of CSP semiconductor device, in which the chip principal surface faces the insulating substrate as it is carried. The flip chip assembly type of semiconductor device is an effective form of technology used to reduce the thickness of the aforementioned package and to improve the heat-releasing property of the chip. However, compared with the wire bonding, the reliability of the connection between the electrode pads and the conductor leads is lower and, because it is hard to see the joint portion, it is difficult to check whether the connection is good.
Another problem with the CSP type of semiconductor device is that the number of the connecting terminals is defined by the chip size. A method that can guarantee the number of the connecting terminals with the highest efficiency is that making use of the BGA (Ball Grid Array) technology with terminals arranged as a 2-dimensional array on the chips principal surface. However, even in this case, since the size of the semiconductor chip is only several millimeters to just over ten millimeters, efforts have to be made to reduce the terminal pitch so as to increase the number of terminals.
The purpose of this invention is to solve the aforementioned problems of the conventional technology by providing a type of semiconductor device with a simple structure that is appropriate for the CSP type of semiconductor device, and that can enable a higher mass productivity and can cut the manufacturing cost.
Another purpose of this invention is to provide a type of semiconductor device using wire bonding, which can reduce the thickness of the package and improve the heat-releasing property of the semiconductor chip.
Yet another purpose of this invention is to provide a CSP type of semiconductor device that can ensure a large number of connecting terminals.